Is: 7088-1973 ( Reaffirmed 2006 ) Indian Standard ( Reaffirmed (ReMiumed NM ) 1999) RECOMMENDED PRACTICE FOR ANODIZING ALUMW1'UM AND ITS ALLOYS (Thid Reprint FEBRUARY 19!74) UDC 669.71 .891..5 @ Copyright 1974 BUREAU OF INDIAN STANDARDS MJ+NAK BHAVAN, 9 BAHADUR SXAH ZAFAR MARC NEW IMiUfl 1MO02 (h- 5 May 1974 IS:7088-1973 hdian Standard RECOMMENDED PRACTKE FOR ANODIZING ALUMINIUM AND ITS ALLOYS Metallic Chairman DR S. RRISHNAMURTHY Indian Telephone Finishes Sectional Committee, SMDC 23 Represetzting Industries Ltd, Bangalore Members International Nickel ( India) 1% Ltd, Bombay DR S. N. ANANT NARAYAN Canning Mitra I-boenix Ltd, Bombay SHRI AHINDRA CHATTERJEE SHRI S. V. K~LKARNI ( Alternate ) Central EIectrocl~en~ical Research Institute ( CSIR), SHRI K. BALAKRIS~ANAN Karaikudi &RI S. R. NATARAIAN ( A&n&? ) Sen-Keleigh Ltd, Asansol SHRI 11). K. CHATTERJEE CHEMIST & METALLURGIST, INTEG- Ministry of Railways RAL COACH FACTORY, PERAMBUR CAEMIST & METALLURDIST II, RESEARCH, DZ~XGNS AND STANDARDS ORGANIZATION, LUCKNOW ( Alfemale ) SQN I,DR hf. C. CHOUDHURY Hindustan Aeronautics Ltcl, Bang&xc SHRI S. V. K. RAO ( Alternate ) Kobinocr EIec:tro-Gilders, Bombay SHRI KANTIL.AL T. DALAL SHRI JAYEXDRA F.. DALAL ( Al/trttnre ) The Indian Tube Company ( 1953 ) Ltcl, Janxhec!pur SHRI I'. N. GANDHI SHRI D. D. BHUPTAXI ( Alternafc ) GENERAL MANAGER, TELECOPY. Director General, Posts and Telegraphs, Sew Delbt FACTORIES DEPUTY GENERAI. MANAGER ( Alternafe ) Bbarat Electronics Ltd, Bangalorc SHRI M. N. KESARI SHRI OK. GURURAJA ( Alternate ) SHRI V. KRISHNAN Directorate General, Ordnance Factories (Ministry of Dcfence ), Calcutta SHRI K. D. BOSE ( Al/ernate ) Ministry of Defencc ( R &. D ) SNRI U. G. K. MENON SHRI S. L. N. ACHARYUI.U ( Alternate ) Jeewanlal ( 1929) Ltd, Calcutta SHRI G. K. MIRCHANDANI Indian Aluminium Company Ltd, Calcutta SHRI B. K. MURTHY SHRI N. GOP~LKRIS~INAN ( Alternate) T.I. Cycles of India, Madras SHRI S. PANCHPAKASAN Guest, Keen, Williams L.td, Calcutta SHRI DILIP PAUL Hindustan Motors Ltd, Calcutta SHRI N. M. RAJU ( Continrred on page 2 ) @ Copyright 1974 BUREAU This publication is protected OF INDIAN STANDARDS the Indian Copyright Act (XIV of 1957 ) and reproduction in whole or in part by any means except with written permission of the publisher shall be deemed to be an infringement of copyright under the said Act. under IS : 7088 - 1973 ( Confinuedfrom puge 1 ) Members Rcprerenting SRRI V. R.WASWAW Ministry of Defcncc ( DC1 ) SHRI M. Y. BORKER (Alternate) SHRI R. K. ROICADE The Premier Automobiles Ltd, Bombay SHRI P. K. ~DESHPANDE ( Alfernufe ) SHRI J. C. NANQIA Arim Metals Industries Pvt Ltd, Calcutta SHRI S. K. NANGIA (Afternute) SHRI N. C. ROY Gcep Flashlight Industries Ltd, Allahabad SHRX v. Trivandrum Rubber Works Ltd, Trivandrum DR R. C. SHARMA Eveready Flashlight Company, Luckuow &RI SURESH R. SHAH Grauer and Weil ( India ) Ltd, Bombay SHRI SUSHIL GOINKA (Alternate) SHRI R. A. SHAH Ronuk Industries Ltd, Bombay KUMARI MRIDULA A. SHAH( Altemata ) SHRI D. S. TANDON National Metallurgical Laboratory ( Jamshcdpur SHRI S. K. RAY ( Allerncrtc) SHRI R. K. SRIVASTAVA, Director General, Is1 ( &-&io Mcmbcr) Deputy Director ( Strut & Met) Secr#fav SHRI S. L. BAM Deputy Director ( Met ), IS1 SHRIK. A. SIDDIQLR ( K. SAMUEL Alternate) CSIR ), Anodized Convener SHRIG. K. MIRCHANDANI Members Aluminium Panel, SMDC 23 : PI6 Jeewanlal ( 1929 ) Ltd, Calcutta SHRIV. K. AGRAWAL Hindustan Aluminium Corporation Ltd, Renukoot CHEMBT &. M E,T A L L u R GI s T, Ministry of Railways INTEGRAL COGH F A c T o R H. SHRIKANTILAL T. DALAL SHRIP. N. DESAI SHRIN. GOPALKRISHNAN SHRI S. K. KHASNOBIS SHRI P. S. MANI SHRI R. K. ROKADE DR R. C. SHARMA PERAMBUR SHRIK. M. SRINIVASAN SIXRI C. D. VARQHESE Kohinoor Electra-Gilders, Bombay Excel1 Process Ltd, Bombay Indian Aluminium Company Ltd, Calcutta Hindustan Motors Ltd, Hooghly Dlrector General, Ordnance Factories (Ministry Defence ), Calcutta The Premier Automobiles Ltd, Bombay The Eveready Flashlight Company, Lucknow Bharat Electronics Ltd, -Bangalore Hindustan Aeronautics Ltd, Bangalore of 2 E:7088-1973 Indian Standard RECOMMENDED PRACTICE FOR ANODIZING ALUMINIUM AND ITS ALLOYS 0. FOREWORD 0.1This Indian Standard was adopted by the Indian Standards Institution on 22 November 1973, after the draft finalized by the Metallic Finishes Sectional Committee had been approved by the Structural and Metals Division Council. 0.2 Anodizing of aluminium and its alloys is widely used for various applications. In order to obtain good anodic coating, it is necessary that correct procedure is followed. This standard has been formulated with a view to providing guidelines for the processes employed for obtaining anodic coatings of approved quality in conformity with IS : 1868-1968* and Applications of anodic coatings produced by these IS : 6057-1970t. processes are given in Appendix A for general guidance. Guidelines for selection of wrought and cast aluminium and its alloys for different types of anodic coatings is given in Appendix B. This standard also recommends the minimum requirements of plant and equipment necessary for producing quality anodic coatings. Such requirements are broadly covered by IS : 2679-1964$. 0.3 The following publications have been consulted during the preparation of thic standard: An&c oxidation of aluminium and its alloys. ( 14 ). Aluminium Federation, London. Information Bulletin Proceedings at the University of Nottingham. September 12 to 14, 1951. Conference on Anodizing Aluminium. The Aluminium Development Association, London. DEF l5 1 Anodizing of aluminium and aluminium alloys. anodizing. ISI BALI ( S L ) Aluminium and its alloys for decorative Bd. Vo124, No. 3; 1972; P 101-7. *Specification tSpecification for anodic coatings for equipment on aluminium (Jksf reuision ). for hard anodic coatings on aluminium. .Y t&commendations for electroplating. 3 IS : 7088 - 1973 1. SCOPE 1.1 This standard covers details of processes generally ducing anodic coatings on aluminium and its alloys. types of processes are covered in this standard: `Type 1 followed for proThe following two Sulphuric or oxalic or chromic acid process - for decorative or protective purposes or both ( see IS : 186%1968" ), and T'ypc 2 ---- Hard anodizing process - for hard anodic coatings suitable for wear resistance and engineering applications ( set! IS : 6057-197OT ). 1.2 A;mlications of anodic coatings Appcldix A for general guidance. I.3 Jntcgral colour in this standard. 2. dURBACE coatings, opaque covered and in this standard coatings are given in barrier are not covered PREPARATION be treated detergent before 2.1 Depending on the finish desired, all parts should anodizing in accordance with the following processes: a) b) c) Dcgreasing in inhibited alkali or non-ionic organic solvent ( see IS : 3194-I 965$ ), Mechanical Brightening polishing through chemical or electrolytic or in an ( see IS : 3656-l 9686 ), and processes. 2.2 For matt and satin fnishes, appropriate processes, such as fluoride etching or acid etching on appropriate aluminium alloys should be employed. NOTS All residues of cleaning material should be removed before anodizing. 3. E+JIPNIENT 3.1 i?or equipment generally made to IS : 2679-196411. required for anodizing, reference may be 3.2 3ZasPension and Jigging - The work piece should be suspended by such means that good electrical contact is maintained throughout the Any metallic parts of a suspension device which makes contreatment. tact with the electrolyte should be of aluminium or titanium. Suspension devices with spring or screw contacts are recommended. Loosely wired as practised in electroplatin g should not normally be used. suspension Rigid parts which are too small to be held in jigs may be packed in perforated canisters of aluminium or titanium for anodizingsuch canisters *Snecification for anodic coatings on aluminium ( first revision ). tSprcification for hard anodic coatings on alum&m. $&de of recommended practice for cleaning of metals prior to electroplating. $Cwle of recommended practice for mechanical polishing of metals for electroplating. l\Recommendations for equipment for electroplating. 4 ISI 7088 - 1973 should incorporate means for maintaining electrical contact between the ,parts and should permit adequate circulation of the electrolyte through their interiors. 3.3 Care should be taken t!rat parts undergoing treatment do not corn& into contact with the tank, stirrer, heating or cooling pipes, or cathode plates, as this may cause breakdown of the film and damage to the parts. The jig design should be such that the parts arc hell cquiclistant from the cathode. 4. 4.1 ANODIZING PROCESSES Pr~ccsr Type 1 4.1 .l Sulphtuic `kid 4.1.1.1 The electrolyte should consist of a solution of sulphuric acid ( see IS : 266.1961* ) within the range of 90 to 4W g/l. Vor general purposes, a solution of sulphuric acid wlthin the range of 165flO g/l at 20 to 25°C at a current density of I.5 A/dn? is rczommcnded. Chloride in the electrolyte should not cxcecd the equivalent of .vYJ g sodium chloride per litre and the dissolved aluminium should not cxcccd the amount correspondin:g with the sulphuric acid concentration as shown in Fig. 1. The operatronal temperature of the clcctrolytc should not exceed 25°C. 50 loo* SlJLPHUFtlC ACID (g/l 500 1 FIG. 1 MAXIMUM ALUMINIUM COVTENT TN SULPHURIC ACID ELECTROLYTES ( AT 15°C ) 4.1.1.2 The electrolyte should be agitated by air free from ~dust and oil or by mechanical means sufficient to maintain a uniform temperature ~__.____... ~--~*Specification for sulphuric acid (rrrird). 5 IS : 7088 - 1973 throughout the electrolytic cell. The electrolyte should be kept clean and free from suspended matter by decantation. `The anodic oxidation is preferably controlled by current density ( normally 1 to I.5 A/dm2 of anode surface ) but may be controlled by voltage after standardizing voltage for each alloy at the respective temperature. Where there is no constant current density and no automatic indicator and controller, it will be a good practice to standardize voltage with respect to current density, temperature and concentration of the electrolyte for every different alloy once every day using a sample panel having 10 percent area of the usual load. 4.1.1.3 The relation of temperature, concentration and voltage for 99.99 percent aluminium and anodizing time and voltage for 99 percent aluminium and some aluminium alloys is given for guidance in Fig., 2 and Fig. 3 respectively. I- 0 10 SULPHURIC 20 ACID, 30 WElGHT PERCENT 40 SO FIG. 2 RELATION OF TEMPERATURE,CONCENTRAT~~ON ANTIVOLTAGE FOR A CURRENT DENSITY OF 1.2 A/dm* IN A SULPHURIC ACID TYPE ELECTROLYTEFOR ALUMINIUM ( 99.99% ) 6 a 7088 - 1973 19 7 Ilfl l1; 611 ul + g > 15- 1L- 13 0 10 20 Ar\10DlSING 30 TIME LO ._ __ 50 bo .. IN MINUTES Fro. 3 VOLTAGES REQUIREDTO MAINTAIN 1*2A/dms FOR VARIOUS ALIJMINIUM ALLOYS ANODIZEDIN 15 PERCENTH,SO, AT 25°C = ( 165 g/l ) 4.1.1.4 The relation between the film thickness and anodizing time at constant current density at constant concentration of sulphuric acid electrolyte and temperature for various alloys is given for guidance in Fig. 4. 4.1.2 Oxalic Acid PTOCGSJ 4.1.2.1 The solution normally used contains 3 to 4 percent oxalic acid, but oxalic acid up to 10 percent has been commercially used. Operation is performed at 30 to 60 V dc, 40 to 60 V ac or a combination of ac and dc. Alloys containing silicon or manganese require slightly higher voltages for comparable results. Temperatures are usually 15 to 35°C and current densities 1 to SA/dm*. The current density is controlled by varying the voltage by standardizing suitably for each alloy. The solution should be agitated vigorously in order that the characteristic light straw colour may be uniform. IS : 7088 - 1973 0 20 LO 60 TIME 80 100 120 ANODISING IN MINUTES FIG. 4 ANODIC COATING THICKNESSESOF ALUNNIUM ALLOYS ( 15 PERCENT H,SO,, l-2 A/dm2, 0 to 120 MINUTES ) 4.1.2.2 The process may yield very thick films if required, but for this purpose sulphuric acid films are normally preferred. Alternating current may be used to produce films with brass yellow to bronze shades, the deeper colours are obtained on the thicker films. Cathodes of carbon, lead, iron or stainless steel are suitable. The operation of oxalic acid anodizing and the control of the composition of the solution (in particular the avoidance of chlorides ) are similar to the sulphuric acid. The film should be sealed as under 7. This process is more expensive both in consumption of chemicals and current than the sulphuric acid process. 4.1.2.3 Mixture of sulphuric and oxalic acid ano_dicing grocess- These processes can be operated at high temperature of 30 to 35°C and therefore require lower extent of refrigeration. Adding of oxalic acid will raise the cost of electrolyte appreciably. NOTE- In order to operate at 30°C, 5 percent by weight of oxalic acid may be added to an electrolyte containing 174 g/l of sulphuric acid. In order to operate the cell at 35OC, 5 percent by-weight of oxalic acid may be added to an electrolyte containing 106 g/l of sulphuric acid. The voltage will have to be increased in order to obtain a current density of 1.5 A/dms. Care should be taken that oxalic acid is thoroughly stirred until it is completely dissolved. 8 IS : 7088- 1973 4.1.3 Chromic Acid l'roccss 4.1.3.1 Statldard process - The electrolyte shall consist of a sdlution containing from 25 to 100 g of chromic acid per litre. The purity of the chromic acid should be riot less than 99.5 percent chromic oxide. Chloride in the electrolyte should not exceed the equivalent of 0.20 g sodium Sulphate in the electrolyte should not exceed the chloride per litre. equivalent of 0.50 g ofsodium sulphate per litre. The free chromic acid content should not be allowed to fall below 25 ~/l. The electrolyte may bc regenerated by the addition of chromic acid provided that the total ~chromium in solution does not exceed 100 g/l calculated as chromic oxide. The operational temperature of the electroiyte should be within the range of 38 to 42°C. Current should be so applied that the voltage across the bath is increased in steps of not more than 5 V from 0 to 40 V in the first 10 minutes, maintained at 40 V for 20 minutes, gradually raised to 50 V in the next These time periods 5 minutes and maintained at 50 V for 5 minutes. should be regarded as minima. The cathode should be of mild steel or stainless steel and should be in the form of plates. The anode-cathode area ratio is not critical, but Values varying from -less chrotiic acid is consumed at the higher ratios. 5 : 1 to 10 : I are generally suitable. 4.1.3.2 Altematice process .for castings - The temperature and voltage conditions given in 4.L3.1 may be unsuitable for anodizing castings of aluminium alloys containins more than 7 percent of copper, nickel and The followmg alternative conditions may be used in such iron combined. cases: The temperature of the electrolyte should be in the range 25 to 30°C. Bath voltage shall be increased in steps of not more than 5 T7 from 0 to 40 V in 10 minutes and the voltage maintained at 40 V for 30 minutes. 4.2 Type 2 -Hard Anodizing Process 4.2.1 Any suitable electrolyte may be used, for example, a 10 percent The chloride content of solution by volume of sulphuric add in water. the electrolyte shall not exceed the equivalent of 0.20 g of sodium chloride per litre. It is necessary to maintain a low temperature at the surface of the work and this is normally achieved by providing a rapid ilow of the cooled electrolyte over all surfaces undergoing treatment. The electrolyte is usually maintained at a temperature between -5°C and +5"C. The cathodes should consist of lead, carbon or other suitable conducting material which is substantially insoluble in the electrolyte. Proper electrical contact to the cathode should be ensured to avoid 9 IS : 7088 - 1973 for hollow parts or one ' burning. Auxiliary cathodes may be necessary having deep recesses to avoid burning. 4.22 The process may be operated with direct current or with a combination of direct and alternating currents. The current density in a typical sulphuric acid electrolyte niay vary from about 2.5 to 4.0 A/dma depending on the process employed land the alloy being treated: likewise the final voltage may vary from about 40 to 120 V depending largely on the thickness of coating required and the alloy. 4.2.3 .Conditions of Anodizing - The conditions of anodizing should be chosen by the anodizer to suit the material being treated and the thickness of coating required. Sample parts of the material should be supplied to the anodizer for trials. 4.2.4 Hard anodizing may impair the surface finish. Surfaces to be treated should have a finish superior to that required on the finished part, unless a final smoothing operation is to be employed. In order to obtain sound coating and to reduce possible damage to it, edges of parts should be radiused; a minimum 0.75 mm radius is recommended. 4.2.5 Where design considerations permit, parts may be hard anodized all over. In other circumstances such as those requiring soft and hard coatings, non-significant areas may be anodized by any Type 1 processes ( unless required to be left untreated ). This should be done by one ~of the following methods: a) Mask the surfaces to be hard anodized with suitable lacquer, wax, acid resistant ink, etc. Anodize by any of Type 1 processes. Remove the masking from the untreated surfacei:. Apply masking to the treated surfaces. Finally anodize by Type 2 process. Remove masking. b) Anodize whole part by any of Type 1 processes. Mask the area not to be hard anodized. Strip anodic coating from the unmasked area. Finally anodize by Type 2 process. Remove the masking. c) Mask all except significant areas. Anodize by Type 2 process. Remove masking. Mask hard anodized areas. Anodize by any of the Type 1 processes. Remove the masking. 4.3 Anodizing of Assemblies Containing Metals Other Than Aluminium - Aluminium parts of composite articles containing other metals should preferably be anodized before assembly. Where this is not possible, the non-aluminium parts should be masked. 4.4 Anodizing of Castings - The suitability of a casting for anodizing, and to some extent the type of process used, depends on the nature of the alloy. sulphuric acid Normally chromic acid process shall be used but in some cases process may be used subject to the requirements given 10 IS : 7088 - 1973 in A-l and A-2. Where castino;s are to be impregnated to seal pores, should be done after the anodizing process has been completed. it NOTE- Chromic acid process is preferred because of the innoruou< nature of any Sulphuric acid process electrolyte which may be retained in the pores of the casting. will, however, treat a somewhat wider range of alloys. Silicon. zinc and magnrsium contents have no marked effect on the suitability for anodizing but certain other alloying elements, notably copper, nickel and iron, may cause diliiculty. In grneral, castings containing more than a total of 7 percent of the latter etcmrnt5 or more than 5 per cent copper are unsuitable for treatment by chromic acid process and castings containing more than 7 percent copper are unsuitable for treatment by sulphuric acid process. Although the nominal composition of a casting may make it appear to be suitable for anodizing, segregation of the constituent may render It unsuitahlr. In borderline casrs, operation of the process at the lowest permissible temperature and voltage, and use of adrquate agitation will be important. 4.5 Re-anodizing - Parts which are to be re-anodized have the anodic coating removed before re-treatment by stripping solution ( see AppenMechanical methods for repolishin, v should not involve the use of diu C ). metallic grit. Where only a portion of the part is to be re-anodized, the original coating o,n the remaining surface may IX retained hy masking the area. NOTEIn all caqcs, spent electrolytes should hr suitably treated before disposal. 4.6 Recommendation on Selection Different Purpose Anodic Finishes tion of wrought and cast alloys, Appendix for protective or decorative anodizing. of Aluminium Alloys for As a general guide to the FelecB gives suitability of the alloys For bright finish aluminium alloys based on at least 99.7 percent purity are recommended. For general purposes aluminium 19500 ( IB) bright finish, but allqys containing silicon and may give reasonably manganese are not successfully bright anodized. 5. RINSING 5.1 Immediately rinsed to remove after removal electrolyte. from the anodizing Cell all parts should be 5.2 Parts which have been anodized by sulphuric/oxali: acid process should be rinsed thoroughly in clean cold running water preferably in a counter current stream. 5.3 Parts which have been anodi7ed by chromic acid process other than for Raw detection, dyeing, painting or bonding. sho:Jd be rinsed in clean cold running water. Parts anodized for flaw detection purposes or parts which are to be dyed should be rinsed in cold water only. For parts anodized for flaw detection purposes, the rinsing should bc brief in order to avoid removal of the chromic acid from defects. Parts anodized as a pv.eparation for bonding or for painting should be rinsed in cold water and then~in clean shot water at a temperature not exceeding 60°C. 11 IS : 7085 - 1973 6. DYEING 6.1 l):_cinx sho:tld normally be done by immersing the article in the dye inlmc:!iatcly nftcr I insing and without allowing the parts to dry. Any . ._ . s!tjtab!c morgamc or proprietary organic dyes may be used for dyeing the film. Cart 4lollld 1~ taken that the light fastntxs value should be in a. c~xclarxc \vitli 1s :I 36%1960':`. :lftcr dyring, the parts should be rinsed in clean c-old I.x:nning jcatcr. 6.2 `l`lvo types of cx~lours, namely, those produced from certain inorganic pigments \vhi~~h lose their colour extremely slowly and are virtually as pcrmancnt as the anodic coating, and those based on organic dyes which pro, idc rc~asonablc colour retention over 5 to 10 years, are applied to anod:c. c:oatin;;s. Slxcessfnl restilts with inorganic pigments depend to a lxgc cstent upon the cxpcrience of the operator in obtaining colour matching. \\`ith the organic dyes laboratory control of the dye bath is an important factor. 6..2.1 LIost of the organic dyestuffs are l!sed in concentration of 0.2 to 10 g/l. `l'emperatures recommcndcd arc often 50 to 6O"C, though some The p1-I value nsaally varies brtivecn 5.5 and 6.5 dyes may bc used cold. L:lt in some dyes the range is 3 to 8. A new dye should be prepared act orOin~ to the maitufacturer's directions. losing distilled water, and if necessary corrected to the proper flH vniue. The IT-1 \.alue of various lots of the same clyc may bc somewhat dinerent. 6.2.1.1 Since th? most important controlling factor to observe using organic: dTcst(Xs is the PH, a pot:*ntiometric PH equipment glass elcctrodcs 1s recomrncndcd for dyi: control. when using 6.2.1.2 S/&e control 0f ~/ZP d~4'c - The concentration of the organic dycstuff is best adjusted by means of a calorimeter. If a calorimeter is not ,l\;ailable, it iq necessary to take a satnple of freshly made dye - say 10 ml and make it up to 500 ml in a measuring cylinder. A similar sample from the proclllction vat is drawn and made up to'500 ml and the two dyes Add water to the freshly prepared dye standard in order to arc comparcd. match colour xvith the production L-at. The original and final volumes of the standard are noted. Ori+nal c______ \-olumc: of .--standard ~_ Final volume of standard x specified found. of concentration = the actual concentration Amount of dye required = specified concentration found concentration x number litres in dye vat. 6.2.2 The dyes should be selected carefully after suitable trial runs in a Iaboratory and evaluating the properties of light fastness, which shall con*Specification for anodic coatings on aluminium (JirH revision ). 12 IS : 7088 - 1973. form to IS : 186%1968*. Also the reaction of dyed articles to_: (a) sealing bath, (b) d'l 1 u t z nitric acid, (c) tartaric acid and sodium and fixing carbonate, and (d) colorrr change on heating, should be obtained before finally selecting tlke dye. 7. SEALLNG 7.1 Parts anodized by Type 1 processes and other undyed sealed bv immersion in one of the fol1owi:i.c solutions indicated against each: temperature a) For UMQeil Coatings Soliltio?l Quantity 1) Demineralized lvater or distilled 70-1oo;gr1 1 parts should be for Deriods and (Minutes) ratur; "C 6-6.5 20-60 94-98 2) Potassium dichromate ( KzCr,07 ) or Sodium &chromate (Na,Cr,O7.?H,O ) Sodium carbonate ( Na,CO, ) Demineralized or distilled water 3) Potaisium dichromate ( K,Cr,07 ) or Sodium dichwmate ( Na,Cr,07.`LH,O ) Demincraiizcd or distilled water b) For D_yd Anodic. Films 1) Nickel acetate Cobalt acetate Boric acid Demineralized water 2) Lead acetate Demineralized water 70-100 g 1 6-7 2-10 94-98 I 18g: 1 litre j 40-60 g I 40-60 g 1 5.5-6.5 5-10 94-98 1 1 litre I 5.5gl l*Og I or distilled 8.5 g > 1 litre 1 6-6.5 15-60 85-95 J or distilled 2.5-5 g] 1 litre t NOTE - Thr @I value of the solution should he maintained by the addition of boric acid or acetic acid. After sraling, the parts should he rinsed in clean cold running \\Tater(except in case of sealing by demineralized or distilled water) and then dried. *Specification for anodic coatings on aluminium (firsf rCuiJiO# ). J 5.5-6 30-60 95- 100 13 IS I 7088 - 1973 APPENDIX APPLICATIONS A-l. TYPE 1 PROCESSES A ( Clauses 0.2 and 1.2 ) A-l.1 Sulphuric or Oxalic Acid Process - These processes are normally suitable for general decorative and protective purposes. These processes are capable of yielding a range of coating thicknesses on most aluminium alloys. It is not, generally, suitable for use on parts containing riveted, lap or folded joints. The coating should be of sufficient thickness ( see IS :1868-1968* ) to provide protection against corrosion and should be properly sealed. A-l.2 Chromic Acid Process -This process yields relatively thin coatings ( of the order of 2.5 microns ). It is the preferred process for the treatment of castings of suitable composition ( see 4.4 ) and for providing a bonding surface for plastics and paint materials. The process should be stipulated where anodizing is required and one or more of the following considerations is paramount: 4 b) 4 4 Minimizing loss of fatigue strength due to anodizing, Treatment of components containing crevices or small blind holes from which electrolyte may be difficult to remove, Detection Treatment of flaws by subsequent of material seepage of the yellow electrolyte, less than 0.25 mm thick. A-2. TYPE 2 HARD ANODIZING PROCESS A-2.1 This process may be used to produce harder and thicker coatings than are obtained by Typ- 1 procrsses and to provide greater resistance to abrasion, heat and electrical breakdown. The thickness of coatings are generally 25 to 75 microns. The treatment may reduce the fatigue strength by about one half. The fatigue strength may largely be restored by sealing the coating in an aqueous dichromate solution, at the cost of some loss of abrasion resistance. __-*Specification for anodic~coatings on aluminium (first rcuision ). 14 IS: 7088.1973 APPENDIX B AND ( Clauses 0.2 and 4.6) SUITABILITY OF WROUGHT AND CAST ALUMPNIUM ITS ALLOYS FOR VARIOUS ANODIC FINISHES Group Desi,qnation -----___---h Cast (see v Wrought ( see IS:617Appendix C t:f i959t ) IS : 737-1965' ) Major Alloying Elementr Suitability Ruling f ----A--`-- for ( &minal ), Percenl Protective Anodizing ; : G Anodizing and Dyeing Brigh; Anodizing Aluminium 19990 19800 19500 19000 ( IA) ( 1B) (1C) ( 1) Al Al Al Al 9999 99.8 99.5 99 : V G G V V G v" V M V : G M U U U M Aluminium manganese Aluminium magnesium 31000 ( N3 ) 52000 53000 55000 57000 54300 ( N4 ( N5 ( N6 ( N7 ( N8 ) ) ) ) ) Mn 1.2 Mg Mrr ME Mg Mg hlg Mg 2.2 3.4 5'0 7.0 4.4, MnO.75 4.5, Mn 0.50 10.2 ; $ V V M E V V G G M M M 5230 ( A5 ) 5500 ( AlO) Aluminiummagnesiumsilicon 63400 ( H9 ) 65400 (Hl9) 65032 (HZ0 ) 64430 ( H30) Mg O-65, Si 0.50 Mg 0.95, Si 0.95 Mg 1.0, Si O-60, Mn 0.50, Cu 0.28 Mg O-90, Si O-95, hiIn 0.70 Cu 1.5, Si 1.0, Mg 0.85 Cu 2.3. Ni 1.0. Mg'0.90, F; 0.90, Si 0.90 Cu 4'1, MgO.80, Mn O-70, Si 0.45 Cu 4-3, MgO.50 Mn 0.75, Si 0.70 Aluminiumcoppermagnesium- 22450 ( HI 1) 22845 ( H12 ) 24534 (H14) 24345 ( H15) G M (D) M 0') M 03 *Specification for wrought aluminium and aluminium alloys, general engineering-purposes ) (J;rsr rcwion ) . ( Since revised ) . TSpe+cation for aluminium and aluminium alloy engmeermg purposes ) ( rruiscd ) . ( Since &vised ). sheet and strip (for ingots and castings ( for general D I Suitable for $Rating : E - Excellent, V = Very good, G = Good, M = Moderate, dark colours only, and U = Unsuitable. IS t 7085 - 1973 Group Designntian ,-+---rr_--_-, Wrought ( see Cast (see Appendix C of IS : 617IS : 737-1965* ) 1959p ) Nujar Alloyirtz Elcmmis ( Numinol ), Percen 1 Suik~bili~ RatGzg$ for c__-_.h--_ Protcr- AnoBright tivc dizing AnoAnodizing and dizing Dyeing G n"z Al G (D) G 2;") u Aluminiumsilicon 43000 (N21 ) 4300 (Al8) 4600 ( A6 ) 4635 ( A9 ) 4520 ( A2 ) 4420 ( A24) 4223 ( A4 or A22 ) 4225 (AK) 2447 ( Al ) 4250 ( A8 ) 2200 (All ) 2550 (Al2 ) 4658 (Al3 2285 (A14) 2148 (A15) ) Si Si Si Yi 5.2 5.2 Il.5 1 I.5 Mn 0.50 Mg 0.40 u" u U u U U U ' Aluminiumsiliconcopper Si 10.2, CIJ 1.6 Si 8.5, CL: 3.5 Si 5.0, Cu 3.3 ? Mn 0.45 Si 5.0, Cu 1.2, i\Jg 0'50 Cn 7.0, Si 3.0, Zn 3.0 Si 4.8, AIR 0.55 Cu 4.5, `1-i O-18 Ca 9.8. Fe 1.0, Mg 0.25 Si 12.0, Xi 2.5, Mg 1.2. Cu 0.90 Cu 4..0, Ki 2.0, Mg 1.4 Cd 2.2, fji I..:. Xi 1.2. hfg 1.1, Fe 1.1, `I`1 018 nr hl G G U G G hl U Alumit:iumzinc-copper U U M U u U M G x&y U M G M CD) G NOTE -Digital designations arc adopted from IS : 6051-1370$. *Specification for wrought aluminium and aluminium alloys, general engineering purposes ) (Jirst revision ). ( Since revised ). sheet and strip (for $Specification for ahnninium and aluminium alloy ingots ancl castings engineering purposes ) ( revised). ( Since revised ). 1, $Rating @ode ( for general : E = Excellent, D = Suitable V = Very good, G = Good, M = Moderate, for dark colours only, and U = Unsuitable. allOyS. i designation of aluminium and its 16 APPENDIX ( Clause 4.5 ) STRIPPING SOLUTIONS FOR THE COATINGS C REMOVAL OF ANODIC C-l. PREFERRED SOLUTION 3.5 percent ( v/v) 2.0 percent ( m/v) Phosphoric acid ( sp gr 1.75 ) Chromic acid Used gently boiling C-2. ALTERNATIVE a) SOLUTIONS Sulphuric acid ( sp gr l-84) Chromic acid ( CrOs ) Water Used at about 50°C I5 percent ( v/v) 5 percent (m/v) Remainder 10 pcrcent ( v/v) 4 percent ( m/v ) 10 percent ( v/v) 1 percent ( m/v) b) Sulphuric acid ( sp gr I.84 ) Potassium fluoride Used at room temperature c) Sulphuric acid ( sp gr 1.84 ) Hydrofluoric acid, commercial ( 50/60 percent HF ) Used at room temperature NOTE - Solutions C-2 (a), (b) and (c) cause greater attack of the basismetal. 17